The present invention is related to a connection confirmation method applied to a packet-based network in which a connection is set like in Multiprotocol Label Switching (MPLS). Instead of a conventional SDH/SONET or optical-based network, the packet-based network is required. As a packet transmission technique, the MPLS has gained attention as a platform that provides not only an IP but also existing services such as FR, ATM, TDM, Ethernet, and the like.
The MPLS is different from a conventional routing process using an IP address and is a packet forwarding technique for forwarding a packet based on identification information called “Label” attached to the packet.
In an example of the MPLS network, a communication path which is called a Label Switched Path (LSP) includes a Label Switching Router (LSR) as a corresponding relay device (switch). A packet is forwarded on the LSP. A label (Push) is attached to the forwarded packet at an entrance of the LSP in a Label Edge Router (LER) that is an LSR positioned on a boundary with a non-MPLS network. In each LSR on the LSP, the label of the packet is replaced and then the packet is forwarded (Swap). In an LER corresponding to an exit, the label attached to the packet is removed (Pop).
As described above, the packet forwarding is made possible by referring to the label attached to the packet in the MPLS network. Therefore, it is possible to reduce a delay time by omitting complicated processing such as reference to the IP address and search of a routing table in each router like in the conventional routing in order to speed up the packet forwarding.
Further, a layering technique is used to achieve scalability of the MPLS network. Thus, it is possible to consolidate the LSPs. If a plurality of labels are layered, that is, the plurality of labels are encapsulated by further attaching another label to the outside of the packet with the label, the LSR refers to only the label on the outside of the packet and performs forwarding without seeing the label information inserted into the packet. Therefore, in a network environment in which MPLS connections increase, it is possible to perform effective connection management by constructing a logical path (a new LSP) of an upper layer in which a plurality of existing LSPs are collected by using this layering technique.
If the LSPs are collected by using the above-described layering technique for maintenance management such as defect detection or communication confirmation of the connections in the MPLS network, it is possible to achieve strength of management and efficiency of the number of management man-hours in specific sections in which the LSPs are collected. Thus, reliability of the connection management can be improved.
On the other hand, for maintenance management in the network in which a packet communication is performed, it is known that the communication of the connection can be confirmed by performing a loopback test between nodes (switches) in the connection.
For example, ITU-T Rec. Y.1711 (February/2004) describes an Operation and Maintenance (OAM) function in an MPLS network and discloses that a loopback is considered to be applied to the MPLS OAM as well.
Further, for maintenance management on a network based on Ethernet, for example, ITU-TRec. Y.1731 (May/2006) discloses that a frame, which includes loopback information on the fact that the MAC address of another node on the same section is set as a destination, is transmitted from the node positioned at the end of the maintenance management section that applies the OAM. Then the communication confirmation can be performed depending on whether or not the frame that includes the loopback information is returned to a transmission source node within a given time.
FIG. 1 illustrates an embodiment that is considered when the OAM technique in the above-described Ethernet is extended to loopback processing on the MPLS network.
In FIG. 1, reference numbers 1 to 5 indicate switches #1 to #5 performing the packet forwarding processing based on labels. The LSP is set to both a direction from the switch #1 to the switch #5 and a direction from the switch #5 to the switch #1. The maintenance management packet transmitted from the switch #1 to the switch #3 includes loopback information and includes an identification label used to identify that the packet is a maintenance management packet, which includes the loopback information, and a label corresponding to the LSP (hereinafter referred to as an LSP label).
When the maintenance management packet is transmitted from the switch #1, the switch #2 replaces the LSP label and then forwards the maintenance management packet. The switch #3 recognizes both the LSP label layer and an identification label layer inside the maintenance management packet and performs the loopback to the switch #1.
On the other hand, FIG. 2 shows an example where the packet forwarding is performed by layering the labels in the part of the connection in which the communication confirmation is desired.
In FIG. 2, reference numbers 1 to 5 indicate the same switches as those of FIG. 1. Further, a new LSP of an upper layer is formed in the section from the switch #2 to the switch #4. That is, when the switch #2 receives the packet transmitted from the switch #1, a new LSP label corresponding to the new LSP (from the switch #2 to the switch #4) is stacked on the outside of the existing LSP label and is then forwarded.
Here, when the maintenance management packet is transmitted to the switch #3 from the switch #1 in the same way as described above, the identification label can not be identified because only the labels of the upper two layers in the switch #3 (the label corresponding to the LSP from the switch #1 to the switch #5 and the label corresponding to the LSP from the switch #2 to the switch #4) are referred to in the switch #3. Therefore, the switch #3 performs the forwarding to the switch #4 without performing the loopback.
Thus, as described above, for example, when the new LSP of the upper layer formed by collecting the plurality of LSPs is formed, there is a problem that the communication confirmation of the LSP of the lower layer cannot be performed effectively.